Many systems that require parallel connection of power supplies use a common signal line between the supplies to control current sharing. Unfortunately, this common signal line constitutes a single point of failure. Others add a resistor in series with each paralleled converter in the supply to give the supply a finite output impedance which acts as a ballast to force current sharing, resulting in increased losses and reduced reliability. Still others electronically simulate the series resistance by actively forcing the voltage to decrease as the load current increases. While the simulation approach eliminates the losses associated with an actual resistor, it disadvantageously requires a current sensor and control circuits as well as communication between primary and secondary sides of the supply, thus requiring either opto-isolators or isolation transformers. In fact, all of these approaches require a number of either opto-isolators or isolation transformers for signal communication between primary and secondary.
Accordingly, it is desirable to minimize the number of isolators in order to provide a very reliable and economical power conversion system. It is also desirable to convert prime input power to a regulated low voltage distribution bus (e.g., 48 Vdc), while providing galvanic isolation between the input bus and the low voltage distribution bus. It is also desirable to provide a converter which is very reliable and simple, has no single point of failure when used in a parallel redundant system (i.e., no communication required between parallel power converters), and which is compatible with a distributed power system, e.g., will run in a stable manner when driving negative resistance loads. In addition, it is also desirable to eliminate any signal communication between primary and secondary that would require isolation devices.